The present invention relates to the general art of structural, bridge and geotechnical engineering, and to the particular field of overfilled arch and/or cut-and-cover structures.
Frequently, overfilled arch structures formed of precast or cast-in-place reinforced concrete are used in the case of bridges to support one pathway over a second pathway, which can be a waterway, a traffic route, or in the case of other structures, a storage space or the like. The terms xe2x80x9coverfilled archxe2x80x9d or xe2x80x9coverfilled bridgexe2x80x9d will be understood from the teaching of the present disclosure, and in general as used herein, an overfilled bridge or an overfilled arch is a bridge formed of arch elements that rest on the ground or on a foundation and has soil or the like resting thereon and thereabout to support and stabilize the structure and in the case of a bridge provide the surface of the second pathway. The arch form is generally arcuate such as cylindrical in circumferential shape, and in particular a prolate shape; however, other shapes can be used. Examples of overfilled bridges are disclosed in U.S. Pat. Nos. 3,482,406 and 4,458,457, the disclosures of which are incorporated herein by reference.
Presently, reinforced concrete overfilled arches are usually constructed by either casting the arch in place or placing precast elements, or a combination of these. These arched structures rest on prepared foundations at the bottom of both sides of the arch. The fill material, at the sides of the arch (backfill material) serves to diminish the outward displacements of the structure when the structure is loaded from above. As used herein, the term xe2x80x9csoilxe2x80x9d is intended to refer to the normal soil, which can be backfill or in situ, located at a site used for a bridge structure, and which would not otherwise adequately support an arch. The terms xe2x80x9cbackfill,xe2x80x9d and xe2x80x9cin situxe2x80x9d will be used to mean such xe2x80x9csoilxe2x80x9d as well.
Soil is not mechanically strong enough to adequately support bridge structures of interest to this invention. Thus, prior art bridge structures have been constructed to transfer forces associated with the structure to walls of the structure and/or large concrete foundations at the base of the wall. Such walls have to be constructed in a manner that will support such forces and thus have special construction requirements. As will be discussed below, such requirements present drawbacks and disadvantages to such prior art structures.
For the prior art structures, the overfilled arches are normally formed such that the foundation level of the arch is at the approximate level of a lower pathway or floor surface of an underground structure over which the arch spans. Referring to FIGS. 1A-1C, it can be understood that prior art systems S1 and S2 include sides or sidewalls SW1 and SW2 which transfer loads from tops T1 and T2 of the arch to foundation F1 and F2. The sides of arch systems S1 and S2 must be sufficiently thick and contain sufficient reinforcement in order to be able to carry these loads and the thereby induced bending moments.
Furthermore, as it is necessary to limit the arch loading and bending actions in the top and sides of prior art overfilled arch systems to an acceptable level, the radius of the arch is in practice restricted. This restriction in arch radius leads to a higher xe2x80x9crisexe2x80x9d R1 and R2 (vertical dimension between the top of clearance profile C1 and C2 of lower pathway surface LS1 or LS2 and crown CR1 and CR2 of the arch) in the arch profile than is often desirable for the economical and practical arrangement of the two pathways and formation of the works surrounding and covering the arch. This results in a lost height LH1 and LH2 which can be substantial in some cases.
Beams or slabs, while needing a larger thickness than arches, do not require this xe2x80x9crisexe2x80x9d and, therefore, can be used for bridges accommodating a smaller height between the top of the clearance profile of the lower pathway and the top of the upper pathway. Arches, despite their economical advantage, often cannot compete with structures using beams or slabs for this reason especially for larger spans. However, the larger thickness may result in an expensive structure whose precast elements may be difficult unwieldy and heavy to transport to a building site. Thus, many of the advantages of this structure may be offset or vitiated.
Furthermore, as indicated in FIGS. 1A-1C, foundations F1 and F2 for the prior art overfilled arch systems must be substantial in order to carry the arch loading indicated in FIG. 1C as AL, and require additional excavation at the base of the arch (generally beneath the lower pathway) to enable their construction. As will be understood from the present disclosure, forces AL can be considered as being circumferential forces, and forces AV can be considered as being vertical forces with forces AH being considered as horizontal forces. Loading forces on the system are a combination of these forces.
For overfilled arches made of precast construction, the incorporation of the required height of the sides or sidewalls of the arch result either in a tall-standing precast element which is difficult and unwieldy to transport and to place or in the requirement of pedestals, such as pedestals F1a shown in FIG. 1A.
It is a main object of the present invention to provide an economical and expeditiously erected overfilled arch structure system and method of forming an overfilled arch structure system.
It is another object of the present invention to provide an arch structure system and method of forming an arch structure system that utilizes soil to create a foundation for the arch structure.
It is another object of the present invention to provide an arch structure and system and method of forming an arch structure and system that does not transfer forces associated with an arch element directly to walls of the arch structure and system whereby the walls are not required to support a significant amount of these forces.
It is another object of the present invention to provide an overfilled arch bridge or other structure and method of construction therefor which enables a minimal arch curvature to be adopted.
It is another object of the present invention to minimize the rise of the arch and hence extend the scope of application of the arch while still maintaining a structural arching action in the arch of the overfilled structure.
It is another object of the present invention to provide an overfilled arch bridge structure and method of construction therefor which enables the sides/sidewalls of the overfilled structure to be of a lighter and therefore more economical design and faster methods of construction as compared to the prior art.
It is another object of the present invention to provide an overfilled arch bridge structure which enables such a structure to be constructed using poor quality backfill material.
It is another object of the present invention to provide an overfilled arch bridge structure and method of construction therefor which enables the footings at the base of the overfilled structure to be smaller than the prior art.
It is another object of the present invention to provide an overfilled arch bridge structure and method of construction therefor which enables the footings at the base of the overfilled structure to be omitted.
It is another object of the present invention to provide an overfilled arch bridge structure and method of construction therefor which enables the footings at the base of the overfilled structure to be reduced to very small dimensions serving only for the erection of sidewalls.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which reduces dependence on large and unwieldy element transportation and reliance on heavy erection cranes as compared to the prior art.
It is another object of the present invention to provide an overfilled arched bridge which is expeditious to produce.
These, and other, objects are achieved by an arched overfilled and/or backfilled structure which includes a shallow arch spanning over a clear space. The sides of the clear space are formed by curved or planar walls. Solidified zones of the backfill material or previously existing (in situ) ground against the footings at the springs, also referred to as ends, of the arch and/or behind the walls form foundation blocks which are in intimate contact with the footings at the arch springs and/or with the upper part of the walls in such a way that the arch delivers all or at least most of its support forces into the aforementioned foundation blocks, drastically reducing the normal forces, shear forces and bending moments in the walls and wall foundations. The arch structure contacts the foundation blocks in a manner that the support forces of the arch are transferred to the foundation blocks rather than to the sidewalls of the system. The resulting advantages of transferring such forces to the foundation blocks rather than to the sidewalls will be understood from the teaching of the present disclosure.
The arched structure system which is formed using precast concrete, or cast-in-place concrete, or a combination of both comprises either:
A plain concrete or reinforced concrete arch resting on arch footings which in turn rest on foundation blocks, the latter being a solidified portion of the backfill or of in situ material located outside of the wall beneath either side of the concrete arch. The concrete arch may be precast, cast-in-place (cip) or a combination. The walls can be formed using mechanically stabilized earth (MSE) or any other type of earth retaining wall system, including but not limited to sheet piles, bored piles, diaphragm walls or an excavated cip, precast or sprayed (shotcrete) concrete wall with or without nails/anchors; or
A continuous, one-piece monolithic frame whereby the top of the frame comprises an arch, and the sides of the frame consist of curved or planar walls, in which the outside surfaces of the arch and top of the walls are shaped such that the arch loads are directed into foundation blocks, the latter being solidified portions of the backfill material or in situ material, located outside the frame sidewalls.
Where precast concrete is used, adjacent precast arch spans may be structurally connected along all or part of the circumferential length.
The foundation blocks of the present invention comprise a material exhibiting sufficient stiffness and strength such that the thrust reactions of the arch can be distributed via the arch footings through the foundation block to the adjacent soil material, such that the displacements of the arch springs are within acceptable limits. Shallow arches, as in the present invention, are particularly susceptible to horizontal outward displacements of the springs. The structure of the present invention ensures that the solid foundations, which are essential for such an arch, can be provided economically.
By enabling a load transfer from the springs of the arch via the arch footings into the foundation blocks, the arch support forces do not need to be transferred into the sidewalls of the earth overfilled system. This characteristic of the system embodying the present invention enables the backfilling of the sidewalls to be combined with the construction of the foundation blocks because all or part of the solidified backfill of the sidewalls or the solidified in situ ground directly constitutes the arch foundation blocks. This also enables more efficient construction procedures to be adopted for construction of the walls, which can be made considerably lighter than prior art systems.
Furthermore, by enabling direct transfer of the arch support forces into the foundation blocks at the top of the sidewalls, it is possible to adopt a flatter arch than is possible and economic for the conventional state of the art. This is because the loads and bending moments transferred into the sidewalls of a conventional overfilled arch are significantly larger for a flatter arch than for a higher (less flat) arch. A flatter arch (smaller arch rise) has the advantage that for a given clearance beneath the sides of the arch, the lost height (see lost height LH1 and LH2 in FIGS. 1A and 1B) can be reduced, and the distance between the lower and upper paths of the overfilled arch system can be reduced, thereby increasing the scope of arch structure application. Thus, the total lost height LH1 or LH2 will be considerably reduced from those values indicated in FIGS. 1A and 1B.
The present invention also includes a cover-and-cut method of such a system.
While a bridge system is discussed herein, it is to be understood that the present invention can be applied to other systems as well without departing from the scope of the present disclosure and invention. For example, any type of underground space (including, but not limited to, shelters, warehouses, storage spaces, backfilled and overfilled, or only backfilled or built into existing in situ ground) can be within the scope of the present invention and disclosure and it is intended that the present invention as defined by the teaching of this disclosure and the claims associated therewith will cover such structures as well.